Manufacturing process tools such as ultraviolet (UV) Laser, near-infrared (NIR) Laser, and infrared (IR) Laser and Blown Ion Plasma, Corona Plasma, Radiofrequency (RF), Pulsed Xenon (Xe) Flash Lamps, and Intense IR Flash Light; all utilize intense photon- and/or electron (i.e., strong photonic and/or electromagnetic field) driven processes to precisely remove (i.e., chemically, mechanically and thermally ablate) top-most surfaces of a variety of organic, inorganic and composite substrates during the production and assembly of high reliability and precision products such as ophthalmic lenses, optical filters, microfluidic devices, medical components, aerospace devices, and many others. The processes employed in these manufacturing tools are collectively termed herein as ionizing-heating radiation or IHR.
IHR technologies share common process control constraints including excessive localized surface heating, melting, deflagration, discoloration, decomposition, and excessive surface particle and film debris generation in regions surrounding and within the contact interface between the IHR beam and/or plume with the substrate surface—referred to as the Heat Affected Zone or HAZ. This is particularly the case for the processing of organic substrates such as polymers, composites, fibers, and skin tissue. Energetic interactions between organic surfaces and IHR beam or plume radiation, electrons, electromagnetic fields, ions, oxidizing gases, and radicals produce plasma-like reactions on the surface which, as a by-product, produce excessive heat, particle, and film contaminations.
Typically, air or gas assist is employed with IHR processes. For Laser processing, an air or nitrogen blow-off gas is used to assist the Laser beam with removal of both heat and ablation debris. For atmospheric corona plasma or blown ion processing, pressurized gas is used to create both reactive ions. An electrified ion delivery plume, called Blown Ion Plasma, delivers the beneficial treatment agents (and hot gases). Atmospheric plasma plumes are typically very hot and cannot be in contact with delicate polymeric substrates containing microscopic surface features for more than fractions of a second. Atmospheric corona plasma or blown ion plume temperatures employing CO2 gas (a preferred atmospheric corona plasma or blown ion fluid in the present invention) exceed the softening or melting point of many common thermoplastics. Gas-assisted IHR processes provide limited cooling capacity in the case of Laser processes, or no cooling capacity in the case of atmospheric corona plasma or blown ion processes.
Moreover, both Laser and AP processing produces surface contaminants as by-products. Heat, radical and UV light generated by-products include, for example, oxidized particles, loosely bound surface layers, and decomposition residues. As such, conventional IHR processes are self-contaminating and do not clean-up after themselves. Mitigation procedures such as using lower IHR energy levels (power/pulse) or performing faster and repeated surface scans to offset deleterious heating affects only slows down material processing rates. As such, conventional IHR-processed substrates typically endure a post-precision cleaning process to achieve adequate cleanliness prior to the next fabrication step. In fact, U.S. Pat. Nos. 5,725,154 and 7,451,941 (exemplary CO2 treatment sprays) developed by the first-named inventor of the present invention has been used to perform this type of secondary precision cleaning operation on IHR-processed polymeric substrates, described herein, and U.S. Pat. Nos. 5,725,154 and 7,451,941 are both incorporated by reference herein. A “CO2 Composite Spray™” (a trademark of CleanLogix LLC, Valencia, Calif.) is an adjustable CO2 particle-fluid jet that is very distinct in form and function from conventional “CO2 Snow” jets which have no compositional or physical control. A CO2 Composite Spray can be controlled to form various sizes of dry ice particles, control particle-fluid concentration, and compose different particle-fluid chemistries and concentrations, as well as control spray pressures and temperatures using a variety of propellant fluids and additives including, but not limited to, clean dry air (CDA), nitrogen, argon, hydrocarbons, volatile methyl siloxanes, and many other possibilities. The distinct capabilities and operational characteristics of CO2 Composite Spray devices suitable for use with the present invention are described in U.S. Pat. Nos. '154 and '941.
The first-named inventor of the present invention has also developed a prior art hybrid surface treatment apparatus and method that addresses various constraints of a particular IHR technology called corona plasma discharge. U.S. Pat. Nos. 7,901,540 and 8,021,489, which are both incorporated by reference herein, describe a coaxial plasma-CO2 spray generator apparatus and method to simultaneously form and apply a corona plasma stream and cleaning particle stream to a substrate surface. The hybrid system of the '540 invention is different in configuration from the present invention; namely it generates both treatment streams internally within a coaxial apparatus and mixes the two streams in the atmosphere immediately exiting the hybrid device spray nozzle (′540, FIG. 3, 124); delivering the resulting composition to the substrate surface below. The '540 invention presents difficulties with regards to being able to independently balance the RF corona plasma power with the CO2 spray composition, particularly when higher plasma power is desired (i.e., increased ion generation). This is required to increase plasma surface treatment rates on the substrate surfaces. Using high-power plasma requires a richer (higher CO2 particle concentration) CO2 Composite Spray to compensate for higher mixing temperatures to prevent premature sublimation of beneficial CO2 cleaning particles. Moreover, the beneficial surface heating derived from the plasma is diminished with higher CO2 particle concentrations. Still moreover, this technique is not useful for removing (ablating) significant amounts of surface material and contaminants thereon in a short period of time.
An alternative hybrid treatment process is needed that can provide more independent treatment stream control, higher IHR operating powers and increased productivity. For example a conventional blown ion plasma system using CO2 gas operates at much higher powers and temperatures, and offers much faster micro-etching rates, but requires significantly improved management of both heat and surface debris contaminant generation to be particularly useful for processing soft or thin substrates such as polymers and composites, as well as other types of challenging substrate materials and geometries discussed herein. Moreover and as described above, IHR manufacturing technology such as Laser, RF Ablation, and Intense IR light also require effective substrate cooling and surface cleaning to provide effective solutions for processing soft substrates.
It has been discovered by the present inventors that mixing a CO2 Composite Spray with a conventional high-powered IHR beam or plume, such as a CO2 Laser beam or an atmospheric blown ion plasma plume, at a precise shearing angle between the IHR beam or plume and the substrate surface, and onto the same surface portion affords advantageous results as compared to prior art gas-assisted and CO2-assisted hybrid surface treatment processes described above. This is particularly the case for the treatment of soft substrate surfaces such as polymers and composites requiring faster and more aggressive surface treatments (at high speed) such as microetching and micromachining. Rather than an expected annihilation or attenuation of the beam or plume functions at the contact point, the CO2 particle stream was found to assist a NIR Laser beam with machining processes and to assist Blown Ion plasma with microetching processes. The resulting new hybrid processes deliver more powerful and effective surface treatment energy (i.e., cleaning agents, etching agents, heat, etc.) through better IHR process optimization and control. The heating and ionizing radiations pass directly through the CO2 Composite Spray into the substrate surface using the novel hybrid spray method herein. The CO2 Composite Spray behaves uniquely in the present invention as a prophylactic particle fluid that cleans and cools while allowing the IHR UV and IR radiation to interact freely with the substrate surface below due to carbon dioxide's advantageous electromagnetic radiation adsorption properties. In the present invention, the present inventors believe that any variety of high-powered IHR devices can be integrated with a CO2 Composite Spray and employed using the novel process described herein. For example, another exemplary hybrid surface treatment process that has been developed using the present invention is NIR and IR Laser technology for micromachining applications.
Finally, the present invention is a cost- and performance-effective alternative to “wet” processes such as organic solvents, and aqueous and semi-aqueous, alkaline and acidic cleaning and etching chemistries to prepare surfaces for coating, bonding, underfilling, and many other applications requiring improved surface adhesion properties. The present invention resolves the constraints of conventional surface preparation and modification technology described above and is summarized below.